Yes, I need everything as real-time as possible. And as previously mentioned, if a position is lost then there is no point in recovering that information because the submarine would be at a new position anyway.
From what I've looked at elsewhere and from the replies on this forum, I feel like UDP is probably my best option. However at this point, I am completely a newbie in using transmission protocols. My experience with Arduino boards is limited to the analog and digital input/output. I don't have any experience with the Ethernet Shield either but I don't feel like that will be too challenging.
How much does this change my programming? Where do I get started?